1. Field of the Invention
The invention relates to a keyboard for electronic measuring instruments, computing devices or the like.
2. Description of the Art
Conventional keyboards for such instruments have a keyboard panel with a number of openings or perforations. Beneath the keyboard panel pushbutton switch elements for actuation by manual pressure are arranged whose manually controlled ends (e.g. in the form of pushbuttons) extend upwards through openings in the keyboard panel, i.e. towards the user.
To avoid permeation of moisture or water into the electrical parts of the keyboard switches and into any circuit portions associated therewith, it is known to use either capacitive switches or to provide for sealing means that prevent passage of moisture or water through the openings of the keyboard panel. Capacitive switches are relatively expensive and/or require much space. Use of sealing means for the keyboard panel is similarly problematic; thus, it is known, for example, to pocket calculators to integrally cover the keyboard with a transparent flexible film or sheet (e.g. of plastic) sealingly fastened at the panel edges. The film or sheet can be provided with a number of protuberances corresponding to the buttons projecting from the keyboard.
A disadvantage of such arrangements is the fact that the film or flexible sheet has to be transparent or else the user cannot read the button designations; alternatively, different markings on the bulges of the covering sheet corresponding to the button designation are needed causing very high tooling and production expenditures so as to be suitable--if at all--for mass production items only.
However, various electronic measuring and/or computing devices that do include, or should conveniently include, a keyboard, such as mobile or stationary monitors for environmental control (air pollution, oxygen content of water in rivers or effluents) are no mass production items but produced in relatively small series and, up to now, no water-proof keyboards have been available that provide for simple and safe operation of such monitors in continuous use and can be produced at reasonable costs even in limited numbers.
It is an object of this invention to provide for such a keyboard having pushbutton switches, i.e. electrical and generally monostable switches requiring a mechanical force of the type exerted by finger pressure for operation, said keyboard having an improved sealing means.
A further object of the invention is to effectively prevent permeation of water through the openings of a keyboard panel. Another object of the invention is a sealed keyboard capable of being manufactured at reasonable costs even if produced in small to medium production series and providing for reliable keyboard operation even under severe weather conditions, e.g. when operated with gloved hands.
Further objects will become apparent as the specification proceeds.